Grant Street beach in Cottesloe has been closed after a whale carcass washed ashore - raising fears it could attract sharks to the area.

The carcass was reported by a member of the public just before 1PM on Sunday, triggering a shark advice alert from authorities.

The Town of Cottesloe closed beaches in the vicinity of Grant Street as a precaution, with the closures to remain in place until the carcass is removed.

Beach goers have been urged to stay out of the water in the affected area, obey directions from rangers and Surf Life Saving WA, and check official shark alerts before heading to the coast.

Anyone who spots a shark is urged to contact Water Police immediately on 9442 8600, with sightings to be published through the SharkSmart warning system.